Axle assembly having an electric motor module and a shift mechanism

ABSTRACT

An axle assembly having an electric motor module, a gear reduction module, and a shift mechanism. The shift mechanism may have a shift collar that may transmit torque from the gear reduction module to a drive pinion. The shift collar may be movable between a first position in which a low range gear ratio is engaged, a second position in which a neutral gear ratio is selected, and a third position in which a high range gear ratio is engaged.

TECHNICAL FIELD

This disclosure relates to an axle assembly that includes an electricmotor module and a shift mechanism that may shift a gear reductionmodule between multiple gear ratios.

BACKGROUND

An axle assembly having an electric motor module is disclosed in U.S.Pat. No. 8,858,379.

SUMMARY

In at least one embodiment, an axle assembly is provided. The axleassembly may include an axle housing, a differential carrier, adifferential carrier cover, an electric motor module, a gear reductionmodule, and a shift mechanism. The differential carrier may be mountedto the axle housing and may rotatably support a differential. Thedifferential carrier cover may be mounted to an end of the differentialcarrier that may be disposed opposite the axle housing. The electricmotor module may be disposed in the differential carrier between theaxle housing and the differential carrier cover. The gear reductionmodule may be disposed adjacent to the differential carrier cover andmay transmit torque from the electric motor module to the differentialvia a drive pinion. The shift mechanism may be moveable to selectivelyengage a low range gear ratio and a high range gear ratio of the gearreduction module.

In at least one embodiment, an axle assembly is provided. The axleassembly may include an axle housing, a differential carrier, adifferential carrier cover, an electric motor module, a gear reductionmodule, and a shift mechanism. The differential carrier may be mountedto the axle housing and may rotatably support a differential. Thedifferential carrier cover may be mounted to an end of the differentialcarrier that may be disposed opposite the axle housing. The electricmotor module may be disposed in the differential carrier between theaxle housing and the differential carrier cover. The gear reductionmodule may transmit torque from the electric motor module to thedifferential via a drive pinion that may be rotatable about an axis. Thegear reduction module may be disposed adjacent to the differentialcarrier cover. The gear reduction module may include a sun gear, a ringgear, a planet gear, and a planet gear carrier. The sun gear may beoperatively connected to the electric motor module and may be rotatableabout the axis. The ring gear may be disposed on the differentialcarrier cover. The planet gear may mesh with the sun gear and the ringgear. The planet gear carrier may rotatably support the planet gear. Theshift mechanism may have a shift collar that may transmit torque fromthe gear reduction module to the drive pinion. The shift collar may bemovable between a first position in which a low range gear ratio isengaged, a second position in which a neutral gear ratio is selected,and a third position in which a high range gear ratio is engaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an axle assembly.

FIG. 2 is a section view of the axle assembly along section line 2-2showing a shift collar in a first position.

FIG. 3 is a section view of the axle assembly showing the shift collarin a second position.

FIG. 4 is a section view of the axle assembly showing the shift collarin a third position.

FIGS. 5-11 are exploded views of the axle assembly.

FIG. 12 is a perspective view of an adapter that may be provided withthe axle assembly.

FIG. 13 is a perspective view of a sun gear that may be provided withthe axle assembly.

FIG. 14 is a perspective view of a shift collar that may be providedwith the axle assembly.

FIG. 15 is a section view of the axle assembly showing a differentialcarrier that has a bearing support wall that is a separate componentfrom the differential carrier.

FIG. 16 is a schematic representation of compound planetary gear setthat may be provided with a gear reduction module.

FIG. 17 is a schematically representation of a countershaft geararrangement that may be provided with the gear reduction module.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Referring to FIG. 1, an example of an axle assembly 10 is shown. Theaxle assembly 10 may be provided with a motor vehicle like a truck, bus,farm equipment, mining equipment, military transport or weaponryvehicle, or cargo loading equipment for land, air, or marine vessels.The motor vehicle may include a trailer for transporting cargo in one ormore embodiments.

The axle assembly 10 may provide torque to one or more traction wheelassemblies that may include a tire mounted on a wheel. One or more axleassemblies may be provided with the vehicle. As is best shown withreference to FIGS. 1 and 2, the axle assembly 10 may include a housingassembly 20, a drive pinion 22, an electric motor module 24, a gearreduction module 26, a shift mechanism 28, a differential assembly 30,and at least one axle shaft 32.

Referring to FIG. 1, the housing assembly 20 may receive variouscomponents of the axle assembly 10. In addition, the housing assembly 20may facilitate mounting of the axle assembly 10 to the vehicle. In atleast one configuration, the housing assembly 20 may include an axlehousing 40 and a differential carrier 42.

The axle housing 40 may receive and support the axle shafts 32. In atleast one embodiment, the axle housing 40 may include a center portion50 and at least one arm portion 52.

The center portion 50 may be disposed proximate the center of the axlehousing 40. The center portion 50 may define a cavity that may receivethe differential assembly 30. As is best shown in FIG. 2, a lower regionof the center portion 50 may at least partially define a sump portionthat may contain lubricant 54. Splashed lubricant 54 may flow down thesides of the center portion 50 and may flow over internal components ofthe axle assembly 10 and gather in the sump portion.

The center portion 50 may include a carrier mounting surface 56. Thecarrier mounting surface 56 may face toward and may engage thedifferential carrier 42. The carrier mounting surface 56 may facilitatemounting of the differential carrier 42 to the axle housing 40. Forexample, the carrier mounting surface 56 may have a set of holes thatmay be aligned with corresponding holes on the differential carrier 42.Each hole may receive a fastener, such as a bolt, that may couple thedifferential carrier 42 to the axle housing 40.

Referring to FIG. 1, one or more arm portions 52 may extend from thecenter portion 50. For example, two arm portions 52 may extend inopposite directions from the center portion 50 and away from thedifferential assembly 30. The arm portions 52 may have substantiallysimilar configurations. For example, the arm portions 52 may each have ahollow configuration or tubular configuration that may extend around thecorresponding axle shaft 32 and may help separate or isolate the axleshaft 32 from the surrounding environment. An arm portion 52 or aportion thereof may be integrally formed with the center portion 50.Alternatively, an arm portion 52 may be separate from the center portion50. In such a configuration, each arm portion 52 may be attached to thecenter portion 50 in any suitable manner, such as by welding or with oneor more fasteners. Each arm portion 52 may define an arm cavity that mayreceive a corresponding axle shaft 32. It is also contemplated that thearm portions 52 may be omitted.

Referring to FIGS. 1 and 2, the differential carrier 42, which may alsobe called a carrier housing, may be mounted to the center portion 50 ofthe axle housing 40. The differential carrier 42 may receive theelectric motor module 24 and may support the differential assembly 30.As is best shown with reference to FIGS. 2 and 5, the differentialcarrier 42 may include one or more bearing supports 60, an exterior wall62, and a bearing support wall 64. In addition, a differential carriercover 66 may be disposed on the differential carrier 42 as is best shownwith reference to FIG. 2.

Referring to FIG. 5, the bearing support 60 may support a roller bearingassembly that may rotatably support the differential assembly 30. Forexample, two bearing supports 60 may be received in the center portion50 and may be located proximate opposite sides of the differentialassembly 30. The bearing support 60 may be provided in variousconfigurations. For example, a bearing support 60 may include a pair oflegs that extend from the differential carrier 42. A bearing cap may bemounted to the legs and may arch over a roller bearing assembly that mayrotatably support the differential assembly 30. As another example, thebearing support 60 may be received in a roller bearing assembly which inturn may support the differential assembly 30.

The exterior wall 62 may extend away from the axle housing 40. Theexterior wall 62 may extend around a first axis 70 and may have agenerally cylindrical configuration. The exterior wall 62 may have anexterior surface 72, an interior surface 74, an end surface 76, and oneor more ports 78.

The exterior surface 72 may face away from the first axis 70 and maydefine an exterior or outside surface of the differential carrier 42.

The interior surface 74 may be disposed opposite the exterior surface72. The interior surface 74 may be disposed at a substantially constantradial distance from the first axis 70 in one or more configurations.

The end surface 76 may be disposed at an end of the differential carrier42 that may be disposed opposite the axle housing 40. The end surface 76may extend between the exterior surface 72 and the interior surface 74and may facilitate mounting of the differential carrier cover 66 as willbe discussed in more detail below.

One or more ports 78 may extend through the exterior wall 62. The ports78 may be configured as a through holes that may extend from theexterior surface 72 to the interior surface 74. The ports 78 may allowcoolant, such as a fluid like water, to flow to and from a water jacketas will be described in more detail below.

Referring to FIGS. 2 and 5, the bearing support wall 64 may extend awayfrom the axle housing 40 and may extend around the first axis 70. Thebearing support wall 64 may be spaced apart from the exterior wall 62such that the exterior wall 62 may extend around the bearing supportwall 64. In addition, the bearing support wall 64 may be radiallypositioned between the first axis 70 and the electric motor module 24.The bearing support wall 64 may cooperate with the exterior wall 62 toat least partially define an outer cavity 80. The outer cavity 80 mayextend around the first axis 70 and may receive the electric motormodule 24 as will be discussed in more detail below. The bearing supportwall 64 may be completely disposed inside the differential carrier 42and may not extend to the differential carrier cover 66. As such, thebearing support wall 64 may be spaced apart from and may not engage thedifferential carrier cover 66. In addition, the bearing support wall 64may define a hole 82. The hole 82 may be disposed opposite the outercavity 80 and may extend around or along the first axis 70.

The bearing support wall 64 may be integrally formed with thedifferential carrier 42, such as is shown in FIG. 2. Alternatively, thebearing support wall 64 may be a separate component from thedifferential carrier 42, such as is shown in FIG. 15. For example, thebearing support wall 64 may include a mounting flange 84 that may extendaway from the first axis 70. The mounting flange 84 may be attached tothe differential carrier 42 with a plurality of fasteners 86, such asbolts. For example, the fasteners 86 may be arranged around the firstaxis 70 and may extend through the mounting flange 84 and into thedifferential carrier 42. The fasteners 86 may be axially positioned orpositioned along the first axis 70 between the axle housing 40 and theelectric motor module 24.

Referring to FIGS. 1 and 2, a differential carrier cover 66 may bedisposed on an end of the differential carrier 42 that may be disposedopposite the axle housing 40. For example, the differential carriercover 66 may be mounted to the end surface 76 of the exterior wall 62.The differential carrier cover 66 may be fixedly attached to theexterior wall 62 in any suitable manner, such as with one or moredifferential carrier cover fasteners 90, such as bolts. As is best shownin FIG. 1, the differential carrier cover 66 may partially define ajunction box 92 that may receive components that may facilitateelectrical connections to the electric motor module 24.

The differential carrier cover 66 may be provided in variousconfigurations. For example, the differential carrier cover 66 mayenclose an end of the differential carrier 42 and may not support a gearreduction module 26 in a configuration where a gear reduction module isnot provided. Alternatively, the differential carrier cover 66 maysupport a gear reduction module 26. For instance, the differentialcarrier cover 66 may have a cover end wall 100 and a cover exterior wall102 as is best shown with reference to FIGS. 2 and 8.

The cover end wall 100 may be disposed on and may be fastened to the endof the differential carrier 42. The cover end wall 100 may define athrough hole 104 that may intersect the first axis 70.

The cover exterior wall 102 may extend from the cover end wall 100 in adirection that extends away from the differential carrier 42. The coverexterior wall 102 may extend around the first axis 70 and may have agenerally cylindrical configuration. The cover exterior wall 102 may atleast partially define a gear cavity 106. The gear cavity 106 may bedisposed outside of the differential carrier 42 and may be disposed onan opposite side of the cover end wall 100 from the differential carrier42.

Referring to FIG. 2, the drive pinion 22 may provide torque to a ringgear 110 that may be provided with the differential assembly 30. Thedrive pinion 22 may extend along and may be rotatable about the firstaxis 70 while the ring gear 110 may be rotatable about a second axis112. In addition, the drive pinion 22 may extend through the hole 82 inthe bearing support wall 64 and through the through hole 104 in thedifferential carrier cover 66. In at least one configuration, such as isbest shown in FIGS. 2, 6 and 7, the drive pinion 22 may include a gearportion 120 and a shaft portion 122.

The gear portion 120 may be disposed at or near an end of the shaftportion 122. The gear portion 120 may have a plurality of teeth that maymate with corresponding teeth on the ring gear 110. The gear portion 120may be integrally formed with the shaft portion 122 or may be providedas a separate component that may be fixedly disposed on the shaftportion 122.

The shaft portion 122 may extend from the gear portion 120 in adirection that extends away from the axle housing 40. As is best shownwith reference to FIGS. 6 and 7, the shaft portion 122 may include anouter surface 130, a threaded portion 132, and a spline 134.

The outer surface 130 may extend from the gear portion 120 and may be anoutside circumference of a portion of the shaft portion 122. One or moredrive pinion bearings 140 may be disposed on the outer surface 130 andmay rotatably support the drive pinion 22. The drive pinion bearings 140may have any suitable configuration. For instance, the drive pinionbearings 140 may be configured as roller bearing assemblies that mayeach include a plurality of rolling elements 142 that may be disposedbetween an inner race 144 and an outer race 146. The inner race 144 mayextend around and may be disposed on the outer surface 130. The outerrace 146 may extend around the rolling elements 142 and may be disposedon bearing support wall 64 of the differential carrier 42 and may bereceived in the hole 82 of the bearing support wall 64. One or morespacer rings 148 may be disposed between the inner races 144 of thedrive pinion bearings 140 to inhibit axial movement of the drive pinionbearings 140 toward each other.

The threaded portion 132 may be axially positioned between the outersurface 130 and the spline 134. A preload nut 150 may be threaded ontothe threaded portion 132 and may apply a preload force on the drivepinion bearings 140.

The spline 134 may be disposed between the threaded portion 132 and anend of the shaft portion 122 that may be disposed opposite the gearportion 120. The spline 134 may include a plurality of teeth. The teethmay be disposed substantially parallel to the first axis 70 and may matewith a corresponding spline on a shift collar of the shift mechanism 28as will be discussed in more detail below. Alternatively, the teeth ofthe spline may mate with a corresponding spline of an adapter that maycouple the drive pinion 22 to a rotor of the electric motor module 24when the gear reduction module 26 and shift mechanism 28 are omitted.

Referring to FIG. 2, the electric motor module 24 may be operativelyconnected to the differential assembly 30 and may provide torque to thedifferential assembly 30 via the drive pinion 22. The electric motormodule 24 may be received inside the differential carrier 42. Forexample, the electric motor module 24 may be received in the outercavity 80 of the differential carrier 42. In addition, the electricmotor module 24 may be axially positioned between the differentialcarrier cover 66 and the axle housing 40. As such, the electric motormodule 24 may be completely received inside of the differential carrier42. Positioning the electric motor module 24 inside the differentialcarrier 42, as opposed to being mounted outside or to an end of thedifferential carrier 42, may help reduce the axial length or standout ofthe axle assembly 10, which may reduce package space, and may positionthe center of mass of the axle assembly 10 closer to the axle housing 40and the second axis 112, which may help with balancing and mounting ofthe axle assembly 10. In at least one configuration, the electric motormodule 24 may include a water jacket 160, a stator 162, a rotor 164, andone or more rotor bearings 166.

Referring to FIGS. 2 and 5, the water jacket 160 may help cool or removeheat from the stator 162. The water jacket 160 may be received in theouter cavity 80 and may extend around the first axis 70 and the stator162. For example, the water jacket 160 may be press fit into the outercavity 80 such that the water jacket 160 may be disposed against theinterior surface 74 of the exterior wall 62 of the differential carrier42. As such, water jacket 160 may be radially positioned between theexterior wall 62 and the stator 162. In at least one configuration, thewater jacket 160 may include a plurality of channels 170 that may extendaround the first axis 70. Coolant may be provided to the water jacket160 via a first port 78 and may exit the water jacket 160 via a secondport 78. For instance, coolant may flow from the first port 78 to thechannels 170, receive heat as the coolant flows through the channels 170and around the first axis 70, and exit at the second port 78. The waterjacket 160 may extend axially from the differential carrier 42 to thedifferential carrier cover 66. The water jacket 160 may be fastened tothe differential carrier cover 66 with one or more fasteners 172, suchas bolts, that may extend through openings in the differential carriercover 66 and into the water jacket 160. As another option, the waterjacket or features of the water jacket like the channels 170 may beintegrally formed with the differential carrier 42 rather than beingprovided as a separate component.

The stator 162 may be fixedly positioned with respect to thedifferential carrier 42. For example, the stator 162 may be receivedinside and may be fixedly disposed on the water jacket 160. The stator162 may extend around the first axis 70 and may include a plurality ofwindings as is known by those skilled in the art.

The rotor 164 may extend around the first axis 70 and may be receivedinside the stator 162. The rotor 164 may be spaced apart from butdisposed in close proximity to the stator 162. The rotor 164 may berotatable about the first axis 70 with respect to the stator 162 and mayinclude magnets or ferromagnetic material that may facilitate thegeneration of electrical current. The rotor 164 may be rotatablysupported by the bearing support wall 64 and may be radially positionedbetween the bearing support wall 64 and the stator 162. The rotor 164may be operatively connected to the drive pinion 22 with or without agear reduction module 26. For instance, the rotor 164 may be operativelyconnected to the drive pinion 22 between the end of the bearing supportwall 64 and the differential carrier cover 66, such as with an adapteras will be discussed in more detail below.

One or more rotor bearings 166 may rotatably support the rotor 164. Inthe configuration shown, two rotor bearings 166 are provided that may bespaced apart from each other. For convenience in reference, the rotorbearing 166 that may be disposed closest to the axle housing 40 may bereferred to as a first rotor bearing while the rotor bearing 166 thatmay be disposed closest to the differential carrier cover 66 may bereferred to as a second rotor bearing. The rotor bearings 166 may haveany suitable configuration. For instance, the rotor bearings 166 may beconfigured as roller bearing assemblies that may each include aplurality of rolling elements 180 that may be disposed between an innerrace 182 and an outer race 184. The inner race 182 may extend around andmay receive the bearing support wall 64. The outer race 184 may extendaround the rolling elements 180 and may be disposed on the rotor 164.

Various components may help position the rotor bearings 166 and inhibitaxial movement of the rotor bearings 166 with respect to the bearingsupport wall 64 and/or inhibit axial movement of the rotor 164 withrespect to the rotor bearings 166. These components may include a spacerring 190, a first retaining member 192, and a second retaining member194.

The spacer ring 190 may be disposed between the rotor bearings 166. Forexample, the spacer ring 190 may extend around the bearing support wall64 and may engage the inner races 182 of the rotor bearings 166 toinhibit axial movement of the rotor bearings 166 toward each other.

The first retaining member 192 may inhibit axial movement of the rotor164 toward the axle housing 40. In at least one configuration, the firstretaining member 192 may be configured as a ring that may extend aroundthe first axis 70 and that may have a generally L-shaped cross-section.The first retaining member 192 may be fixedly disposed on the rotor 164in any suitable manner. For example, one or more fasteners 196, such asbolts, may couple the first retaining member 192 to the rotor 164. Thefirst retaining member 192 may extend to the outer race 184 of the firstrotor bearing 166, thereby inhibiting axial movement.

The second retaining member 194 may inhibit axial movement of the rotor164 and one or more rotor bearings 166 away from the axle housing 40. Inat least one configuration, the second retaining member 194 may beconfigured as a ring that may extend around the first axis 70 and thatmay have a generally L-shaped cross-section. The second retaining member194 may be fixedly disposed on the bearing support wall 64 in anysuitable manner. For example, one or more fasteners 198, such as bolts,may couple the second retaining member 194 to an end of the bearingsupport wall 64. The second retaining member 194 may extend to the innerrace of the second rotor bearing 166, thereby inhibiting axial movement.

Referring to FIG. 2, the gear reduction module 26, if provided, maytransmit torque from the electric motor module 24 to the differentialassembly 30. As such, the gear reduction module 26 may be operativelyconnected to the electric motor module 24 and the differential assembly30. The gear reduction module 26 may be primarily disposed outside ofthe differential carrier 42, thereby providing a modular constructionthat may be mounted to the differential carrier 42 when gear reductionis desired. Such a configuration may allow for a standardizedconstruction of the differential carrier 42 and/or the electric motormodule 24.

The gear reduction module 26 may be disposed adjacent to and may bemounted to the differential carrier cover 66. In addition, the gearreduction module 26 may be primarily received or at least partiallyreceived in the gear cavity 106 of the differential carrier cover 66. Assuch, the gear reduction module 26 may be primarily disposed outside ofthe differential carrier 42.

The gear reduction module 26 may be provided in various configurations,such as planetary gear set configurations and non-planetary gear setconfigurations. Referring to FIGS. 2-9, an example of a gear reductionmodule 26 that has a planetary gear set configuration is shown. In sucha configuration, the gear reduction module may include a sun gear 200,at least one planet gear 202, a planetary ring gear 204, and a planetgear carrier 206.

Referring to FIGS. 2, 8 and 13, the sun gear 200 may be disposedproximate the center of the planetary gear set and may be rotatableabout the first axis 70. In addition, the sun gear 200 may extendthrough the through hole 104 in the cover end wall 100 of thedifferential carrier cover 66. As is best shown primarily with referenceto FIG. 13, the sun gear 200 may be a hollow tubular body that mayinclude a first end surface 210, a second end surface 212, a sun gearhole 214, an enlarged portion 216, a sun gear spline 218, a first gearportion 220, a second gear portion 222, and a seal mounting surface 224.

The first end surface 210 may be disposed at an end of the sun gear 200that may face toward the axle housing 40. The first end surface 210 maybe disposed in the differential carrier 42.

The second end surface 212 may be disposed at an end of the sun gear 200that may face away from the axle housing 40. As such, the second endsurface 212 may be disposed opposite the first end surface 210. Thesecond end surface 212 may be disposed in the gear cavity 106 of thedifferential carrier cover 66.

The sun gear hole 214 may extend from the first end surface 210 to thesecond end surface 212. The sun gear hole 214 may extend along and maybe centered about the first axis 70. The drive pinion 22 may extendthrough the sun gear hole 214 and may be spaced apart from the sun gear200.

The enlarged portion 216 may be a portion of the sun gear hole 214 thatmay extend from the second end surface 212 to the first gear portion220. The enlarged portion 216 may have a larger diameter than the firstgear portion 220 and a larger diameter than a shift collar that mayselectively couple the gear reduction module 26 to the drive pinion 22as will be discussed in more detail below.

The sun gear spline 218 may facilitate coupling of the sun gear 200 toan adapter as will be discussed in more detail below. In at least oneconfiguration, the sun gear spline 218 may be disposed opposite the sungear hole 214 and may extend from or may be disposed adjacent to thefirst end surface 210. As such, the sun gear spline 218 may be receivedinside the adapter 250. It is also contemplated that the sun gear spline218 may be disposed in the sun gear hole 214. In such a configuration,the adapter may be received inside the first gear portion 220.

The first gear portion 220 may be disposed in the sun gear hole 214between the first end surface 210 and the enlarged portion 216. Teeth ofthe first gear portion 220 may be arranged around the first axis 70 andmay extend toward the first axis 70.

The second gear portion 222 may be disposed proximate the second endsurface 212 of the sun gear 200. The second gear portion 222 may haveteeth that may mesh with teeth of the planet gears 202. The teeth of thesecond gear portion 222 may be arranged around the first axis 70 and mayextend away from the first axis 70.

The seal mounting surface 224 may be disposed between the sun gearspline 218 and the second gear portion 222. The seal mounting surface224 may be a generally smooth surface that may face away from the firstaxis 70 and that may extend around the first axis 70.

Referring to FIGS. 2, 8 and 9, one or more planet gears 202 may berotatably disposed between the sun gear 200 and the planetary ring gear204. Each planet gear 202 may have a hole and a set of teeth. The holemay be a through hole that may extend through the planet gear 202. Theset of teeth may be disposed opposite the hole. The set of teeth maymesh with teeth of the second gear portion 222 of the sun gear 200 andteeth on the planetary ring gear 204. Each planet gear 202 may beconfigured to rotate about a different planet pinion axis. The planetpinion axes may extend substantially parallel to the first axis 70.

The planetary ring gear 204 may extend around the first axis 70 and mayreceive the planet gears 202. The planetary ring gear 204 may include aplurality of teeth that may extend toward the first axis 70 and may meshwith teeth on the planet gears 202. The planetary ring gear 204 may befixedly positioned with respect to the differential carrier cover 66 andthe first axis 70. For example, the planetary ring gear 204 may bereceived in the gear cavity 106 of the differential carrier cover 66 andmay be fixedly disposed in the differential carrier cover 66 such thatan outside circumference of the planetary ring gear 204 may be disposedon a side of the cover exterior wall 102 that faces toward the firstaxis 70.

The planet gear carrier 206 may be rotatable about the first axis 70 andmay rotatably support the planet gears 202. In at least oneconfiguration, the planet gear carrier 206 may include a planet gearcarrier hole 230, a planet gear carrier gear portion 232, a planet gearcarrier flange 234, and one or more pins 236.

The planet gear carrier hole 230 may be a through hole that may extendthrough planet gear carrier 206. The planet gear carrier hole 230 mayextend along and may be centered about the first axis 70.

The planet gear carrier gear portion 232 may be disposed in the planetgear carrier hole 230. Teeth of the planet gear carrier gear portion 232may be arranged around the first axis 70 and may extend toward the firstaxis 70.

The planet gear carrier flange 234 may be supposed on a side of theplanet gear carrier 206 that may face away from the planet gears 202. Aroller bearing assembly 238 may extend around the planet gear carrierflange 234 to rotatably support the planet gear carrier 206. The rollerbearing assembly 238 may be disposed between the planet gear carrierflange 234 and a shift mechanism housing 300 that may be disposed on thedifferential carrier cover 66.

One or more pins 236 may rotatably support the planet gears 202. Forexample, a pin 236 may extend into or through the hole in acorresponding planet gear 202. A roller bearing may extend around eachpin 236 and may be disposed between the pin 236 and a correspondingplanet gear 202 in one or more embodiments.

Referring to FIG. 16, an example of a gear reduction module that has acompound planetary gear set is shown. A compound planetary gear setconfiguration may include a sun gear 200, a planetary ring gear 204, anda planet gear carrier 206 as previously described. One or more planetgears 202′ may be rotatably disposed between the sun gear 200 and theplanetary ring gear 204. Each planet gear 202′ may have a hole, a firstset of teeth 226′, and a second set of teeth 228′. The hole may be athrough hole that may extend through the planet gear 202′. The first setof teeth 226′ may be disposed opposite the hole and may mesh with teethof the second gear portion 222 of the sun gear 200. The second set ofteeth 228′ may also be disposed opposite the hole and may mesh with theteeth of the planetary ring gear 204. The second set of teeth 228′ maybe arranged at a greater radial distance from the rotational axis of theplanet gear 202′ than the first set of teeth 226′.

Referring to FIG. 17, an example of a gear reduction module that has acountershaft gear arrangement is shown. In a countershaft arrangement, aplurality of gear sets, such as two sets of gears may be axiallypositioned adjacent to each other. The first set of gears may include afirst inner gear 240 that may mesh with teeth on at least one firstouter gear 242. The second set of gears may include a second inner gear244 that may mesh with teeth on at least one second outer gear 246. Thefirst inner gear 240 and the second inner gear 244 may be rotatableabout the first axis 70. The first inner gear 240 may have a smallerdiameter than the second inner gear 244. The first outer gear 242 mayhave a larger diameter than the second outer gear 246. A first outergear 242 may be connected to a corresponding second outer gear 246 witha countershaft 248, which may also be called a layshaft, such that thefirst outer gear 242 and the second outer gear 246 may rotate about acommon axis that may be spaced apart from the first axis 70. A clutchcollar may selectively engage the first inner gear 240 or the secondinner gear 244 to provide different gear ratios to the drive pinion 22.It is also contemplated that a countershaft gear arrangement may includea single countershaft rather than multiple countershafts as shown inFIG. 17.

Referring to FIGS. 2, 6, 7 and 12, an adapter 250 may couple theelectric motor module 24 to the gear reduction module 26. For example,the adapter 250 may couple the rotor 164 to the sun gear 200. Theadapter 250 may be disposed inside the differential carrier 42 and maybe axially positioned between the axle housing 40 and the differentialcarrier cover 66. In at least one configuration, the adapter 250 mayinclude a tubular body 252 and a flange portion 254.

The tubular body 252 may have a first end 260 and a second end 262 thatmay be disposed opposite the first end 260. The tubular body 252 maydefine an adapter hole 264 that may extend from the first end 260 to thesecond end 262. The adapter hole 264 may be a through hole that mayextend along and may be centered about the first axis 70. The drivepinion 22 may extend through the adapter hole 264 and may be spacedapart from the adapter 250. The sun gear 200 may be received in theadapter hole 264. For example, the tubular body 252 may include anadapter spline 266 that may be disposed in the adapter hole 264. Theadapter spline 266 may have teeth that may be arranged around the firstaxis 70 and may extend toward the first axis 70. The teeth of theadapter spline 266 may mate with the teeth of the sun gear spline 218such that the adapter 250 may rotate about the first axis 70 with thesun gear 200 and the rotor 164.

The flange portion 254 may be disposed between the first end 260 and thesecond end 262 of the tubular body 252. The flange portion 254 mayextend from the tubular body 252 in a direction that extends away fromthe first axis 70. The flange portion 254 may be fixedly coupled to therotor 164. For instance, the flange portion 254 may include a set ofholes that may be arranged around the first axis 70 and that may receivefasteners 268, such as bolts, that may extend through the holes tocouple the flange portion 254 to the rotor 164.

Referring to FIGS. 2, 6 and 7, an adapter seal 270 may be disposed onthe tubular body 252. The adapter seal 270 may be disposed proximate thefirst end 260 of the tubular body 252 and may extend around the tubularbody 252. The adapter seal 270 may extend from the adapter 250 to thebearing support wall 64 of the differential carrier 42. As such, theadapter seal 270 may separate the outer cavity 80 of the differentialcarrier 42 from the hole 82 in the bearing support wall 64 to inhibitlubricant 54 from entering the outer cavity 80 and from flowing to theelectric motor module 24.

Referring to FIGS. 2, 8 and 9, a sun gear seal 272 may also be providedto inhibit lubricant 54 from entering the outer cavity 80. The sun gearseal 272 may be disposed on and may extend around the seal mountingsurface 224 of the sun gear 200. The sun gear seal 272 may extend fromthe sun gear 200 to the differential carrier cover 66. For example, thesun gear seal 272 may be received in the through hole 104 of the coverend wall 100 of the differential carrier cover 66.

Referring to FIGS. 2, 6 and 7 a rotary encoder 280 may be associatedwith the electric motor module 24. The rotary encoder 280 may bedisposed near the electric motor module 24 and may also be isolated fromthe lubricant 54 due to the sealing provided by the adapter seal 270 andthe sun gear seal 272. The rotary encoder 280 may be provided to detectrotation of the rotor 164. In at least one configuration, the rotaryencoder 280 may include a rotary disc 282 and a sensor 284.

The rotary disc 282 may rotate about the first axis 70 with the rotor164. The rotary disc 282 may be provided in any suitable location. Inthe configuration shown, the rotary disc 282 is fixedly mounted to thesecond end 262 of the tubular body 252 of the adapter 250 with fasteners286, such as bolts. As such, the rotary disc 282 may extend around thesun gear 200 and may rotate with the rotor 164 and the adapter 250. Inaddition, the rotary disc 282 may be axially positioned between theflange portion 254 of the adapter 250 and the differential carrier cover66. As such, the rotary disc 282 may be positioned between the bearingsupport wall 64 of the differential carrier 42 and the differentialcarrier cover 66. The rotary disc 282 may have a non-cylindrical outersurface that may face away from the first axis 70 that may include aplurality of protrusions that may extend away from the first axis 70.

The sensor 284 may extend around the rotary disc 282. The sensor 284 maydetect rotation of the rotary disc 282 by detecting the presence orabsence of the protrusions of the rotary disc 282. The sensor 284 maycommunicate with an electronic controller that may control operation ofthe electric motor module 24. The sensor 284 may have any suitableconfiguration. In the configuration shown, the sensor 284 is configuredas a ring that may extend around the first axis 70. The sensor 284 maybe fixedly mounted to a mounting plate 290 which in turn may be fixedlymounted to the differential carrier cover 66 with one or more fasteners292, such as bolts, which are best shown in FIG. 8.

Referring to FIG. 2, the shift mechanism 28 may be disposed at an end ofthe axle assembly 10 that may be disposed opposite the axle housing 40.For example, the shift mechanism 28 may be disposed on the differentialcarrier cover 66.

The gear reduction module 26 may cooperate with the shift mechanism 28to provide a desired gear reduction ratio to change the torque providedfrom the electric motor module 24 to the differential assembly 30, andhence to the axle shafts 32 of the axle assembly 10. For example, thegear reduction module 26 may provide a first drive gear ratio and asecond drive gear ratio. The first drive gear ratio, which may bereferred to as a low range gear ratio, may provide gear reduction fromthe electric motor module 24 to the differential assembly 30 and henceto the axle shafts 32. As a nonlimiting example, the first drive gearratio may provide a 2:1 gear ratio or more. The first drive gear ratiomay provide increased torque to a vehicle traction wheel as compared tothe second drive gear ratio. The second drive gear ratio, which may bereferred to as a high range gear ratio, may provide a different gearreduction ratio or lesser gear reduction ratio than the first drive gearratio. For instance, the second drive gear ratio may provide a 1:1 gearratio. The second drive gear ratio may facilitate faster vehiclecruising or a cruising gear ratio that may help improve fuel economy. Inaddition, a neutral drive gear ratio or neutral position may be providedin which torque may not be provided to the differential assembly 30 bythe electric motor module 24.

Referring to FIGS. 2, 10 and 11, the gear reduction module 26 mayinclude a shift mechanism housing 300, an end plate 302, a shift collar304, and an actuator 306.

The shift mechanism housing 300 may be disposed on the differentialcarrier cover 66 and may be mounted to a side of the differentialcarrier cover 66 that may be disposed opposite the differential carrier42. For example, the shift mechanism housing 300 may be mounted to thecover exterior wall 102 of the differential carrier cover 66 with one ormore fasteners 310, such as bolts. The shift mechanism housing 300 maycooperate with the differential carrier cover 66 to define the gearcavity 106. In addition, the shift mechanism housing 300 may facilitatemounting of the actuator 306 and may at least partially define a shiftmechanism cavity 312 that may at least partially receive the shiftcollar 304. As is best shown in FIG. 2, the shift mechanism housing 300may rotatably support the planet gear carrier 206 via the roller bearingassembly 238.

The end plate 302, which may also be referred to as an end cap, may bedisposed on an end of the shift mechanism housing 300 that may bedisposed opposite the axle housing 40. For example, the end plate 302may be mounted to the shift mechanism housing 300 with a plurality offasteners 320, such as bolts. The end plate 302 may rotatably supportthe shift collar 304. For example, the end plate 302 may have a supportfeature 322 that may be disposed on an interior surface of the end plate302 and that may extend toward the differential carrier cover 66. Thesupport feature 322 may be centered about the first axis 70 and may besubstantially cylindrical in one or more configurations. The supportfeature 322 may be received in the shift collar 304 and may rotatablysupport the shift collar 304 such that the shift collar 304 may berotatable about the support feature 322. The support feature 322 may beintegrally formed with the end plate 302 or may be provided as aseparate component.

Referring to FIG. 2, the shift collar 304 may be at least partiallyreceived in the shift mechanism housing 300. For instance, the shiftcollar 304 may be at least partially received in the shift mechanismhousing 300 and may extend through components of the gear reductionmodule 26, such as the planet gear carrier 206. In at least oneconfiguration such as is best shown in FIG. 14, the shift collar 304 mayinclude a shift collar hole 330, a shift collar spline 332, a shiftcollar groove 334, and a shift collar gear 336.

The shift collar hole 330 may extend through the shift collar 304 andmay extend around the first axis 70. The shift collar hole 330 mayreceive the shaft portion 122 of the drive pinion 22.

The shift collar spline 332 may be disposed in the shift collar hole 330and may be axially positioned near a first end of the shift collar 304that may face toward the differential carrier 42. The shift collarspline 332 may extend toward the first axis 70 and may mate with thespline 134 of the drive pinion 22. The mating splines may allow theshift collar 304 to move in an axial direction or along the first axis70 while inhibiting rotation of the shift collar 304 about the firstaxis 70 with respect to the drive pinion 22. Thus, the shift collar 304may be rotatable about the first axis 70 with the drive pinion 22.

The shift collar groove 334 may be disposed proximate a second end ofthe shift collar 304 that may face toward the end plate 302. The shiftcollar groove 334 face away from the first axis 70 and may extend aroundthe first axis 70. The shift collar groove 334 may receive a linkage340, such as a shift fork, that may operatively connect the shift collar304 to the actuator 306.

The shift collar gear 336 may be disposed between the first end and thesecond end of the shift collar 304. The shift collar gear 336 may haveteeth that may be arranged around the first axis 70 and that may extendaway from the first axis 70.

The shift collar 304 may be movably disposed on the drive pinion 22 andthe support feature 322. More specifically, the shift collar 304 maymove axially or in a direction that extends along the first axis 70between a first position, a second position, and a third position. Thesepositions are illustrated in FIGS. 2-4.

Referring to FIG. 2, the shift collar 304 is shown in the firstposition. In the first position, the shift collar 304 may couple theplanet gear carrier 206 to the drive pinion 22. For example, the teethof the shift collar gear 336 may mesh with the teeth of the planet gearcarrier gear portion 232 of the planet gear carrier 206. As such, torquethat is provided by the electric motor module 24 may be transmittedthrough the adapter 250, sun gear 200, planet gears 202, and planet gearcarrier 206 to the shift collar 304 and from shift collar 304 to thedrive pinion 22. The shift collar 304 may be disposed in the shiftmechanism housing 300 and in the differential carrier cover 66 and maynot extend into the differential carrier 42 when in the first positionor a low range gear ratio is selected.

Referring to FIG. 3, the shift collar 304 is shown in a second positionor neutral position. The second position may be axially positionedbetween the first position and the third position. In the secondposition, the shift collar 304 may not couple the gear reduction module26 to the drive pinion 22. For example, the teeth of the shift collargear 336 may not mesh with the teeth of the sun gear 200 or the planetgear carrier 206. As such, torque that is provided by the electric motormodule 24 may not be transmitted to the shift collar 304 or the drivepinion 22. The shift collar 304 may be disposed closer to the axlehousing 40 when in the second position than when in the first position.The shift collar 304 may be axially positioned such that a portion ofthe shift collar 304 may extend through the differential carrier cover66 and into the differential carrier 42 when the second position orneutral gear ratio is selected.

Referring to FIG. 4, the shift collar 304 is shown in the thirdposition. In the first position, the shift collar 304 may couple the sungear 200 to the drive pinion 22. For example, the teeth of the shiftcollar gear 336 may mesh with the teeth of the first gear portion 220 ofthe sun gear 200. As such, torque that is provided by the electric motormodule 24 may be transmitted through the adapter 250 and sun gear 200 tothe shift collar 304 and from shift collar 304 to the drive pinion 22.The shift collar 304 may be disposed closer to the axle housing 40 whenin the third position than when in the second position. The shift collar304 may be axially positioned such that a portion of the shift collar304 may extend through the differential carrier cover 66 and into thedifferential carrier 42 when the third position or high range gear ratiois selected.

It is also contemplated that the shift collar may be omitted such thatthe gear reduction module may provide a single gear ratio rather thanmultiple gear ratios. For example, the planet gear carrier 206 may becoupled to the drive pinion 22 to provide a low range gear ratio withouta high range gear ratio.

The actuator 306 may be disposed on the shift mechanism housing 300. Theactuator 306 may move the shift collar 304 along the first axis 70between the first, second, and third positions. For example, theactuator 306 may be coupled to the shift collar 304 with the linkage340. The actuator 306 may be of any suitable type. For example, theactuator 306 may be an electrical, electromechanical, pneumatic orhydraulic actuator.

An electronic controller may control operation of the actuator 306 andhence movement of the shift collar 304. An example of shifting of theshift collar 304 will now be discussed in the context of an axleassembly 10 that has a gear reduction module 26 having a planetary gearconfiguration. Starting with the shift collar 304 in the first position,the electronic controller may receive one or more inputs that may beindicative of speed (e.g., rotational speed of the rotor 164) and/ortorque (e.g., torque provided by the electric motor). Shifting of theshift collar 304 from the first position to the second position orneutral position may be commenced when the speed and/or torque exceedpredetermined threshold levels. Torque on the shift collar 304 may betemporarily relieved or reduced by controlling the rotational speed ofthe electric motor so that the shift collar 304 may more easily beactuated from the first position to the second position. The shiftcollar 304 may then be actuated from the second position to the thirdposition. More specifically, the rotational speed of the shift collar304 may be synchronized with the rotational speed of the sun gear 200and then the actuator 306 may be controlled to move the shift collar 304from the second position to the third position. The steps may begenerally reversed to move the shift collar 304 from the third positionto the first position. For instance, torque on the shift collar 304 maybe temporarily relieved or reduced to allow the shift collar 304 to movefrom the third position to the second position and rotational speed ofthe shift collar 304 and planet gear carrier 206 may be synchronized toallow the shift collar 304 to move from the second position to the firstposition.

Referring to FIG. 2, the flow of lubricant 54 in the axle assembly 10will now be described in more detail. Lubricant 54 may flow between theaxle housing 40 in the shift mechanism housing 300 without entering theouter cavity 80 due to the sealing provided by the adapter seal 270 andthe sun gear seal 272. As such, lubricant 54 that is splashed by thering gear 110 may flow through the hole 82 in the differential carrier42 to reach the gear cavity 106 and the shift mechanism housing 300. Forexample, lubricant 54 may flow between the axle housing 40 and the gearcavity 106 by flowing through the hole 82, drive pinion bearings 140,the adapter hole 264 of the adapter 250, and the sun gear hole 214 ofthe sun gear 200. Lubricant 54 may then be directed to the planet gears202 in the roller bearing assembly 238 that may rotatably support theplanet gear carrier 206. Some lubricant 54 may also accumulate in thebottom of the gear cavity 106 as shown.

Referring to FIG. 2, the differential assembly 30 may be at leastpartially received in the center portion 50 of the housing assembly 20.The differential assembly 30 may transmit torque to the vehicle tractionwheel assemblies and permit the traction wheel assemblies to rotate atdifferent velocities. The differential assembly 30 may be operativelyconnected to the axle shafts 32 and may permit the axle shafts 32 torotate at different rotational speeds in a manner known by those skilledin the art. As such, the differential assembly 30 may receive torque viathe ring gear 110 and provide torque to the axle shafts 32.

Referring to FIGS. 1 and 2, the axle shafts 32 may transmit torque fromthe differential assembly 30 to corresponding traction wheel assemblies.For example, two axle shafts 32 may be provided such that each axleshaft 32 extends through a different arm portion 52 of axle housing 40.The axle shafts 32 may extend along and may be rotated about the secondaxis 112 by the differential assembly 30. Each axle shaft 32 may have afirst end and a second end. The first end may be operatively connectedto the differential assembly 30. The second end may be disposed oppositethe first end and may be operatively connected to a wheel end assemblythat may have a wheel hub that may support a wheel. Optionally, gearreduction may be provided between an axle shaft and a wheel.

The axle assembly described above may allow an electric motor module tobe assembled to or retrofitted on an existing axle housing. In addition,a gear reduction module or gear reduction module accompanied by a shiftmechanism may optionally be provided to provide gear reduction that mayimprove vehicle traction at low speeds or on increased road grades. Themodular end-to-end positioning of the gear reduction module and theshift mechanism may allow gear reduction modules and shift mechanisms tobe added to or removed from an axle assembly to meet operatingconditions or performance requirements. Moreover, the modularconstruction may allow components such as the differential carrier,differential carrier cover, and shift mechanism housing to be made of alighter weight material, such as aluminum, as compared to the axlehousing, which may help reduce weight and improve fuel economy. Theremovable end plate may also allow the axle assembly to be coupled to adrive shaft which may allow the axle assembly to be provided as part ofa parallel hybrid driveline rather than an all-electric configuration.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover, a gear reduction module that is disposed adjacent to the differential carrier cover, wherein the gear reduction module transmits torque from the electric motor module to the differential via a drive pinion, the gear reduction module including a sun gear that is operatively connected to the electric motor module and rotatable about the axis, a planetary ring gear, a planet gear that meshes with the sun gear and the planetary ring gear, and a planet gear carrier that rotatably supports the planet gear; and a shift mechanism that has a shift collar that is moveable to selectively engage a low range gear ratio or a high range gear ratio of the gear reduction module, wherein the shift collar is received inside the sun gear.
 2. The axle assembly of claim 1 wherein the shift mechanism is received in a shift mechanism housing that is mounted to the differential carrier cover and is disposed opposite the differential carrier.
 3. The axle assembly of claim 2 wherein the shift collar is at least partially received in the shift mechanism housing, is moveably disposed on the drive pinion, and is rotatable with the drive pinion.
 4. The axle assembly of claim 3 further comprising an actuator that is disposed on the shift mechanism housing that actuates the shift collar along the axis.
 5. The axle assembly of claim 3 wherein the shift collar is axially positioned such that a portion of the shift collar is disposed in the differential carrier housing when the high range gear ratio is selected.
 6. The axle assembly of claim 1 wherein the shift collar is axially positioned outside of the differential carrier when the low range gear ratio is engaged.
 7. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover; a gear reduction module that is disposed adjacent to the differential carrier cover, wherein the gear reduction module transmits torque from the electric motor module to the differential via a drive pinion; a shift mechanism that is moveable to selectively engage a low range gear ratio or a high range gear ratio of the gear reduction module, wherein the shift mechanism includes a shift collar that is at least partially received in the shift mechanism housing, wherein the shift collar is moveably disposed on the drive pinion and is rotatable about an axis with the drive pinion; and an end plate disposed on an end of the shift mechanism housing that is disposed opposite the axle housing, wherein the shift collar is rotatably supported by the end plate.
 8. The axle assembly of claim 7 wherein the shift collar defines a shift collar hole that extends through the shift collar and that receives the drive pinion.
 9. The axle assembly of claim 8 wherein the end plate has a support feature that is received in the shift collar and that rotatably supports the shift collar such that the shift collar is rotatable about the support feature.
 10. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover; a gear reduction module that is disposed adjacent to the differential carrier cover, wherein the gear reduction module transmits torque from the electric motor module to the differential via a drive pinion; and a shift mechanism that is moveable to selectively engage a low range gear ratio or a high range gear ratio of the gear reduction module, wherein the shift mechanism includes a shift collar that is at least partially received in the shift mechanism housing, wherein the shift collar is moveably disposed on the drive pinion and is rotatable about an axis with the drive pinion and the shift collar is axially positioned such that a portion of the shift collar extends through the differential carrier cover when a neutral gear ratio is selected.
 11. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover; a gear reduction module that transmits torque from the electric motor module to the differential via a drive pinion that is rotatable about an axis, wherein the gear reduction module is disposed adjacent to the differential carrier cover and includes: a sun gear that is operatively connected to the electric motor module and is rotatable about the axis; a planetary ring gear that is disposed on the differential carrier cover; a planet gear that meshes with the sun gear and the planetary ring gear; and a planet gear carrier that rotatably supports the planet gear; and a shift mechanism that has a shift collar that transmits torque from the gear reduction module to the drive pinion, wherein the shift collar is moveable between a first position in which a low range gear ratio is engaged, a second position in which a neutral gear ratio is selected, and a third position in which a high range gear ratio is engaged.
 12. The axle assembly of claim 11 wherein the shift collar couples the planet gear carrier to the drive pinion when the low range gear ratio is engaged.
 13. The axle assembly of claim 11 wherein the shift collar couples the sun gear to the drive pinion when the high range gear ratio is engaged.
 14. The axle assembly of claim 11 wherein the second position is axially positioned between the first position and the third position.
 15. The axle assembly of claim 11 wherein the shift collar is received inside the sun gear.
 16. The axle assembly of claim 15 wherein the shift collar is received inside the planet gear carrier.
 17. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover; a gear reduction module that transmits torque from the electric motor module to the differential via a drive pinion that is rotatable about an axis, wherein the gear reduction module is disposed adjacent to the differential carrier cover and includes: a sun gear that is operatively connected to the electric motor module and is rotatable about the axis; a planetary ring gear that is disposed on the differential carrier cover; a planet gear that meshes with the sun gear and the planetary ring gear; and a planet gear carrier that rotatably supports the planet gear; and a shift mechanism that has a shift collar that transmits torque from the gear reduction module to the drive pinion, wherein the shift collar is moveable between a first position in which a low range gear ratio is engaged, a second position in which a neutral gear ratio is selected, and a third position in which a high range gear ratio is engaged, and the shift collar does not couple the gear reduction module to the drive pinion when the neutral gear ratio is selected.
 18. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover; a gear reduction module that transmits torque from the electric motor module to the differential via a drive pinion that is rotatable about an axis, wherein the gear reduction module is disposed adjacent to the differential carrier cover and includes: a sun gear that is operatively connected to the electric motor module and is rotatable about the axis; a planetary ring gear that is disposed on the differential carrier cover; a planet gear that meshes with the sun gear and the planetary ring gear; and a planet gear carrier that rotatably supports the planet gear; and a shift mechanism that has a shift collar that transmits torque from the gear reduction module to the drive pinion, wherein the shift collar is moveable between a first position in which a low range gear ratio is engaged, a second position in which a neutral gear ratio is selected, and a third position in which a high range gear ratio is engaged, wherein the first position is axially positioned further from the axle housing than the third position.
 19. An axle assembly comprising: an axle housing; a differential carrier that is mounted to the axle housing and rotatably supports a differential; a differential carrier cover that is mounted to an end of the differential carrier that is disposed opposite the axle housing; an electric motor module disposed in the differential carrier between the axle housing and the differential carrier cover; a gear reduction module that transmits torque from the electric motor module to the differential via a drive pinion that is rotatable about an axis, wherein the gear reduction module is disposed adjacent to the differential carrier cover and includes: a sun gear that is operatively connected to the electric motor module and is rotatable about the axis; a planetary ring gear that is disposed on the differential carrier cover; a planet gear that meshes with the sun gear and the planetary ring gear; and a planet gear carrier that rotatably supports the planet gear; and a shift mechanism that has a shift collar that transmits torque from the gear reduction module to the drive pinion, wherein the shift collar is moveable between a first position in which a low range gear ratio is engaged, a second position in which a neutral gear ratio is selected, and a third position in which a high range gear ratio is engaged, wherein the shift collar includes a shift collar gear that is arranged around the axis and that faces away from the axis, and the sun gear has a sun gear hole that extends along the axis from a first end surface of the sun gear to a second end surface of the sun gear and a first gear portion that is disposed between the first end surface and the second end surface, wherein the shift collar gear meshes with the first gear portion when the shift collar is in the third position.
 20. The axle assembly of claim 19 wherein the sun gear has an enlarged portion that extends from the first gear portion to the second end surface and that has a larger diameter than the shift collar gear, wherein the shift collar gear is disposed in the enlarged portion when the shift collar is in the second position. 